1 //===- BitstreamWriter.h - Low-level bitstream writer interface -*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This header defines the BitstreamWriter class. This class can be used to 11 // write an arbitrary bitstream, regardless of its contents. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #ifndef BITSTREAM_WRITER_H 16 #define BITSTREAM_WRITER_H 17 18 #include "llvm/ADT/StringRef.h" 19 #include "llvm/ADT/SmallVector.h" 20 #include "llvm/Bitcode/BitCodes.h" 21 #include <vector> 22 23 namespace llvm { 24 25 class BitstreamWriter { 26 SmallVectorImpl<char> &Out; 27 28 /// CurBit - Always between 0 and 31 inclusive, specifies the next bit to use. 29 unsigned CurBit; 30 31 /// CurValue - The current value. Only bits < CurBit are valid. 32 uint32_t CurValue; 33 34 /// CurCodeSize - This is the declared size of code values used for the 35 /// current block, in bits. 36 unsigned CurCodeSize; 37 38 /// BlockInfoCurBID - When emitting a BLOCKINFO_BLOCK, this is the currently 39 /// selected BLOCK ID. 40 unsigned BlockInfoCurBID; 41 42 /// CurAbbrevs - Abbrevs installed at in this block. 43 std::vector<BitCodeAbbrev*> CurAbbrevs; 44 45 struct Block { 46 unsigned PrevCodeSize; 47 unsigned StartSizeWord; 48 std::vector<BitCodeAbbrev*> PrevAbbrevs; 49 Block(unsigned PCS, unsigned SSW) : PrevCodeSize(PCS), StartSizeWord(SSW) {} 50 }; 51 52 /// BlockScope - This tracks the current blocks that we have entered. 53 std::vector<Block> BlockScope; 54 55 /// BlockInfo - This contains information emitted to BLOCKINFO_BLOCK blocks. 56 /// These describe abbreviations that all blocks of the specified ID inherit. 57 struct BlockInfo { 58 unsigned BlockID; 59 std::vector<BitCodeAbbrev*> Abbrevs; 60 }; 61 std::vector<BlockInfo> BlockInfoRecords; 62 63 // BackpatchWord - Backpatch a 32-bit word in the output with the specified 64 // value. 65 void BackpatchWord(unsigned ByteNo, unsigned NewWord) { 66 Out[ByteNo++] = (unsigned char)(NewWord >> 0); 67 Out[ByteNo++] = (unsigned char)(NewWord >> 8); 68 Out[ByteNo++] = (unsigned char)(NewWord >> 16); 69 Out[ByteNo ] = (unsigned char)(NewWord >> 24); 70 } 71 72 void WriteByte(unsigned char Value) { 73 Out.push_back(Value); 74 } 75 76 void WriteWord(unsigned Value) { 77 unsigned char Bytes[4] = { 78 (unsigned char)(Value >> 0), 79 (unsigned char)(Value >> 8), 80 (unsigned char)(Value >> 16), 81 (unsigned char)(Value >> 24) }; 82 Out.append(&Bytes[0], &Bytes[4]); 83 } 84 85 unsigned GetBufferOffset() const { 86 return Out.size(); 87 } 88 89 unsigned GetWordIndex() const { 90 unsigned Offset = GetBufferOffset(); 91 assert((Offset & 3) == 0 && "Not 32-bit aligned"); 92 return Offset / 4; 93 } 94 95 public: 96 explicit BitstreamWriter(SmallVectorImpl<char> &O) 97 : Out(O), CurBit(0), CurValue(0), CurCodeSize(2) {} 98 99 ~BitstreamWriter() { 100 assert(CurBit == 0 && "Unflused data remaining"); 101 assert(BlockScope.empty() && CurAbbrevs.empty() && "Block imbalance"); 102 103 // Free the BlockInfoRecords. 104 while (!BlockInfoRecords.empty()) { 105 BlockInfo &Info = BlockInfoRecords.back(); 106 // Free blockinfo abbrev info. 107 for (unsigned i = 0, e = static_cast<unsigned>(Info.Abbrevs.size()); 108 i != e; ++i) 109 Info.Abbrevs[i]->dropRef(); 110 BlockInfoRecords.pop_back(); 111 } 112 } 113 114 /// \brief Retrieve the current position in the stream, in bits. 115 uint64_t GetCurrentBitNo() const { return GetBufferOffset() * 8 + CurBit; } 116 117 //===--------------------------------------------------------------------===// 118 // Basic Primitives for emitting bits to the stream. 119 //===--------------------------------------------------------------------===// 120 121 void Emit(uint32_t Val, unsigned NumBits) { 122 assert(NumBits && NumBits <= 32 && "Invalid value size!"); 123 assert((Val & ~(~0U >> (32-NumBits))) == 0 && "High bits set!"); 124 CurValue |= Val << CurBit; 125 if (CurBit + NumBits < 32) { 126 CurBit += NumBits; 127 return; 128 } 129 130 // Add the current word. 131 WriteWord(CurValue); 132 133 if (CurBit) 134 CurValue = Val >> (32-CurBit); 135 else 136 CurValue = 0; 137 CurBit = (CurBit+NumBits) & 31; 138 } 139 140 void Emit64(uint64_t Val, unsigned NumBits) { 141 if (NumBits <= 32) 142 Emit((uint32_t)Val, NumBits); 143 else { 144 Emit((uint32_t)Val, 32); 145 Emit((uint32_t)(Val >> 32), NumBits-32); 146 } 147 } 148 149 void FlushToWord() { 150 if (CurBit) { 151 WriteWord(CurValue); 152 CurBit = 0; 153 CurValue = 0; 154 } 155 } 156 157 void EmitVBR(uint32_t Val, unsigned NumBits) { 158 uint32_t Threshold = 1U << (NumBits-1); 159 160 // Emit the bits with VBR encoding, NumBits-1 bits at a time. 161 while (Val >= Threshold) { 162 Emit((Val & ((1 << (NumBits-1))-1)) | (1 << (NumBits-1)), NumBits); 163 Val >>= NumBits-1; 164 } 165 166 Emit(Val, NumBits); 167 } 168 169 void EmitVBR64(uint64_t Val, unsigned NumBits) { 170 if ((uint32_t)Val == Val) 171 return EmitVBR((uint32_t)Val, NumBits); 172 173 uint64_t Threshold = 1U << (NumBits-1); 174 175 // Emit the bits with VBR encoding, NumBits-1 bits at a time. 176 while (Val >= Threshold) { 177 Emit(((uint32_t)Val & ((1 << (NumBits-1))-1)) | 178 (1 << (NumBits-1)), NumBits); 179 Val >>= NumBits-1; 180 } 181 182 Emit((uint32_t)Val, NumBits); 183 } 184 185 /// EmitCode - Emit the specified code. 186 void EmitCode(unsigned Val) { 187 Emit(Val, CurCodeSize); 188 } 189 190 //===--------------------------------------------------------------------===// 191 // Block Manipulation 192 //===--------------------------------------------------------------------===// 193 194 /// getBlockInfo - If there is block info for the specified ID, return it, 195 /// otherwise return null. 196 BlockInfo *getBlockInfo(unsigned BlockID) { 197 // Common case, the most recent entry matches BlockID. 198 if (!BlockInfoRecords.empty() && BlockInfoRecords.back().BlockID == BlockID) 199 return &BlockInfoRecords.back(); 200 201 for (unsigned i = 0, e = static_cast<unsigned>(BlockInfoRecords.size()); 202 i != e; ++i) 203 if (BlockInfoRecords[i].BlockID == BlockID) 204 return &BlockInfoRecords[i]; 205 return 0; 206 } 207 208 void EnterSubblock(unsigned BlockID, unsigned CodeLen) { 209 // Block header: 210 // [ENTER_SUBBLOCK, blockid, newcodelen, <align4bytes>, blocklen] 211 EmitCode(bitc::ENTER_SUBBLOCK); 212 EmitVBR(BlockID, bitc::BlockIDWidth); 213 EmitVBR(CodeLen, bitc::CodeLenWidth); 214 FlushToWord(); 215 216 unsigned BlockSizeWordIndex = GetWordIndex(); 217 unsigned OldCodeSize = CurCodeSize; 218 219 // Emit a placeholder, which will be replaced when the block is popped. 220 Emit(0, bitc::BlockSizeWidth); 221 222 CurCodeSize = CodeLen; 223 224 // Push the outer block's abbrev set onto the stack, start out with an 225 // empty abbrev set. 226 BlockScope.push_back(Block(OldCodeSize, BlockSizeWordIndex)); 227 BlockScope.back().PrevAbbrevs.swap(CurAbbrevs); 228 229 // If there is a blockinfo for this BlockID, add all the predefined abbrevs 230 // to the abbrev list. 231 if (BlockInfo *Info = getBlockInfo(BlockID)) { 232 for (unsigned i = 0, e = static_cast<unsigned>(Info->Abbrevs.size()); 233 i != e; ++i) { 234 CurAbbrevs.push_back(Info->Abbrevs[i]); 235 Info->Abbrevs[i]->addRef(); 236 } 237 } 238 } 239 240 void ExitBlock() { 241 assert(!BlockScope.empty() && "Block scope imbalance!"); 242 243 // Delete all abbrevs. 244 for (unsigned i = 0, e = static_cast<unsigned>(CurAbbrevs.size()); 245 i != e; ++i) 246 CurAbbrevs[i]->dropRef(); 247 248 const Block &B = BlockScope.back(); 249 250 // Block tail: 251 // [END_BLOCK, <align4bytes>] 252 EmitCode(bitc::END_BLOCK); 253 FlushToWord(); 254 255 // Compute the size of the block, in words, not counting the size field. 256 unsigned SizeInWords = GetWordIndex() - B.StartSizeWord - 1; 257 unsigned ByteNo = B.StartSizeWord*4; 258 259 // Update the block size field in the header of this sub-block. 260 BackpatchWord(ByteNo, SizeInWords); 261 262 // Restore the inner block's code size and abbrev table. 263 CurCodeSize = B.PrevCodeSize; 264 BlockScope.back().PrevAbbrevs.swap(CurAbbrevs); 265 BlockScope.pop_back(); 266 } 267 268 //===--------------------------------------------------------------------===// 269 // Record Emission 270 //===--------------------------------------------------------------------===// 271 272 private: 273 /// EmitAbbreviatedLiteral - Emit a literal value according to its abbrev 274 /// record. This is a no-op, since the abbrev specifies the literal to use. 275 template<typename uintty> 276 void EmitAbbreviatedLiteral(const BitCodeAbbrevOp &Op, uintty V) { 277 assert(Op.isLiteral() && "Not a literal"); 278 // If the abbrev specifies the literal value to use, don't emit 279 // anything. 280 assert(V == Op.getLiteralValue() && 281 "Invalid abbrev for record!"); 282 } 283 284 /// EmitAbbreviatedField - Emit a single scalar field value with the specified 285 /// encoding. 286 template<typename uintty> 287 void EmitAbbreviatedField(const BitCodeAbbrevOp &Op, uintty V) { 288 assert(!Op.isLiteral() && "Literals should use EmitAbbreviatedLiteral!"); 289 290 // Encode the value as we are commanded. 291 switch (Op.getEncoding()) { 292 default: llvm_unreachable("Unknown encoding!"); 293 case BitCodeAbbrevOp::Fixed: 294 if (Op.getEncodingData()) 295 Emit((unsigned)V, (unsigned)Op.getEncodingData()); 296 break; 297 case BitCodeAbbrevOp::VBR: 298 if (Op.getEncodingData()) 299 EmitVBR64(V, (unsigned)Op.getEncodingData()); 300 break; 301 case BitCodeAbbrevOp::Char6: 302 Emit(BitCodeAbbrevOp::EncodeChar6((char)V), 6); 303 break; 304 } 305 } 306 307 /// EmitRecordWithAbbrevImpl - This is the core implementation of the record 308 /// emission code. If BlobData is non-null, then it specifies an array of 309 /// data that should be emitted as part of the Blob or Array operand that is 310 /// known to exist at the end of the record. 311 template<typename uintty> 312 void EmitRecordWithAbbrevImpl(unsigned Abbrev, SmallVectorImpl<uintty> &Vals, 313 StringRef Blob) { 314 const char *BlobData = Blob.data(); 315 unsigned BlobLen = (unsigned) Blob.size(); 316 unsigned AbbrevNo = Abbrev-bitc::FIRST_APPLICATION_ABBREV; 317 assert(AbbrevNo < CurAbbrevs.size() && "Invalid abbrev #!"); 318 BitCodeAbbrev *Abbv = CurAbbrevs[AbbrevNo]; 319 320 EmitCode(Abbrev); 321 322 unsigned RecordIdx = 0; 323 for (unsigned i = 0, e = static_cast<unsigned>(Abbv->getNumOperandInfos()); 324 i != e; ++i) { 325 const BitCodeAbbrevOp &Op = Abbv->getOperandInfo(i); 326 if (Op.isLiteral()) { 327 assert(RecordIdx < Vals.size() && "Invalid abbrev/record"); 328 EmitAbbreviatedLiteral(Op, Vals[RecordIdx]); 329 ++RecordIdx; 330 } else if (Op.getEncoding() == BitCodeAbbrevOp::Array) { 331 // Array case. 332 assert(i+2 == e && "array op not second to last?"); 333 const BitCodeAbbrevOp &EltEnc = Abbv->getOperandInfo(++i); 334 335 // If this record has blob data, emit it, otherwise we must have record 336 // entries to encode this way. 337 if (BlobData) { 338 assert(RecordIdx == Vals.size() && 339 "Blob data and record entries specified for array!"); 340 // Emit a vbr6 to indicate the number of elements present. 341 EmitVBR(static_cast<uint32_t>(BlobLen), 6); 342 343 // Emit each field. 344 for (unsigned i = 0; i != BlobLen; ++i) 345 EmitAbbreviatedField(EltEnc, (unsigned char)BlobData[i]); 346 347 // Know that blob data is consumed for assertion below. 348 BlobData = 0; 349 } else { 350 // Emit a vbr6 to indicate the number of elements present. 351 EmitVBR(static_cast<uint32_t>(Vals.size()-RecordIdx), 6); 352 353 // Emit each field. 354 for (unsigned e = Vals.size(); RecordIdx != e; ++RecordIdx) 355 EmitAbbreviatedField(EltEnc, Vals[RecordIdx]); 356 } 357 } else if (Op.getEncoding() == BitCodeAbbrevOp::Blob) { 358 // If this record has blob data, emit it, otherwise we must have record 359 // entries to encode this way. 360 361 // Emit a vbr6 to indicate the number of elements present. 362 if (BlobData) { 363 EmitVBR(static_cast<uint32_t>(BlobLen), 6); 364 assert(RecordIdx == Vals.size() && 365 "Blob data and record entries specified for blob operand!"); 366 } else { 367 EmitVBR(static_cast<uint32_t>(Vals.size()-RecordIdx), 6); 368 } 369 370 // Flush to a 32-bit alignment boundary. 371 FlushToWord(); 372 373 // Emit each field as a literal byte. 374 if (BlobData) { 375 for (unsigned i = 0; i != BlobLen; ++i) 376 WriteByte((unsigned char)BlobData[i]); 377 378 // Know that blob data is consumed for assertion below. 379 BlobData = 0; 380 } else { 381 for (unsigned e = Vals.size(); RecordIdx != e; ++RecordIdx) { 382 assert(Vals[RecordIdx] < 256 && "Value too large to emit as blob"); 383 WriteByte((unsigned char)Vals[RecordIdx]); 384 } 385 } 386 387 // Align end to 32-bits. 388 while (GetBufferOffset() & 3) 389 WriteByte(0); 390 } else { // Single scalar field. 391 assert(RecordIdx < Vals.size() && "Invalid abbrev/record"); 392 EmitAbbreviatedField(Op, Vals[RecordIdx]); 393 ++RecordIdx; 394 } 395 } 396 assert(RecordIdx == Vals.size() && "Not all record operands emitted!"); 397 assert(BlobData == 0 && 398 "Blob data specified for record that doesn't use it!"); 399 } 400 401 public: 402 403 /// EmitRecord - Emit the specified record to the stream, using an abbrev if 404 /// we have one to compress the output. 405 template<typename uintty> 406 void EmitRecord(unsigned Code, SmallVectorImpl<uintty> &Vals, 407 unsigned Abbrev = 0) { 408 if (!Abbrev) { 409 // If we don't have an abbrev to use, emit this in its fully unabbreviated 410 // form. 411 EmitCode(bitc::UNABBREV_RECORD); 412 EmitVBR(Code, 6); 413 EmitVBR(static_cast<uint32_t>(Vals.size()), 6); 414 for (unsigned i = 0, e = static_cast<unsigned>(Vals.size()); i != e; ++i) 415 EmitVBR64(Vals[i], 6); 416 return; 417 } 418 419 // Insert the code into Vals to treat it uniformly. 420 Vals.insert(Vals.begin(), Code); 421 422 EmitRecordWithAbbrev(Abbrev, Vals); 423 } 424 425 /// EmitRecordWithAbbrev - Emit a record with the specified abbreviation. 426 /// Unlike EmitRecord, the code for the record should be included in Vals as 427 /// the first entry. 428 template<typename uintty> 429 void EmitRecordWithAbbrev(unsigned Abbrev, SmallVectorImpl<uintty> &Vals) { 430 EmitRecordWithAbbrevImpl(Abbrev, Vals, StringRef()); 431 } 432 433 /// EmitRecordWithBlob - Emit the specified record to the stream, using an 434 /// abbrev that includes a blob at the end. The blob data to emit is 435 /// specified by the pointer and length specified at the end. In contrast to 436 /// EmitRecord, this routine expects that the first entry in Vals is the code 437 /// of the record. 438 template<typename uintty> 439 void EmitRecordWithBlob(unsigned Abbrev, SmallVectorImpl<uintty> &Vals, 440 StringRef Blob) { 441 EmitRecordWithAbbrevImpl(Abbrev, Vals, Blob); 442 } 443 template<typename uintty> 444 void EmitRecordWithBlob(unsigned Abbrev, SmallVectorImpl<uintty> &Vals, 445 const char *BlobData, unsigned BlobLen) { 446 return EmitRecordWithAbbrevImpl(Abbrev, Vals, StringRef(BlobData, BlobLen)); 447 } 448 449 /// EmitRecordWithArray - Just like EmitRecordWithBlob, works with records 450 /// that end with an array. 451 template<typename uintty> 452 void EmitRecordWithArray(unsigned Abbrev, SmallVectorImpl<uintty> &Vals, 453 StringRef Array) { 454 EmitRecordWithAbbrevImpl(Abbrev, Vals, Array); 455 } 456 template<typename uintty> 457 void EmitRecordWithArray(unsigned Abbrev, SmallVectorImpl<uintty> &Vals, 458 const char *ArrayData, unsigned ArrayLen) { 459 return EmitRecordWithAbbrevImpl(Abbrev, Vals, StringRef(ArrayData, 460 ArrayLen)); 461 } 462 463 //===--------------------------------------------------------------------===// 464 // Abbrev Emission 465 //===--------------------------------------------------------------------===// 466 467 private: 468 // Emit the abbreviation as a DEFINE_ABBREV record. 469 void EncodeAbbrev(BitCodeAbbrev *Abbv) { 470 EmitCode(bitc::DEFINE_ABBREV); 471 EmitVBR(Abbv->getNumOperandInfos(), 5); 472 for (unsigned i = 0, e = static_cast<unsigned>(Abbv->getNumOperandInfos()); 473 i != e; ++i) { 474 const BitCodeAbbrevOp &Op = Abbv->getOperandInfo(i); 475 Emit(Op.isLiteral(), 1); 476 if (Op.isLiteral()) { 477 EmitVBR64(Op.getLiteralValue(), 8); 478 } else { 479 Emit(Op.getEncoding(), 3); 480 if (Op.hasEncodingData()) 481 EmitVBR64(Op.getEncodingData(), 5); 482 } 483 } 484 } 485 public: 486 487 /// EmitAbbrev - This emits an abbreviation to the stream. Note that this 488 /// method takes ownership of the specified abbrev. 489 unsigned EmitAbbrev(BitCodeAbbrev *Abbv) { 490 // Emit the abbreviation as a record. 491 EncodeAbbrev(Abbv); 492 CurAbbrevs.push_back(Abbv); 493 return static_cast<unsigned>(CurAbbrevs.size())-1 + 494 bitc::FIRST_APPLICATION_ABBREV; 495 } 496 497 //===--------------------------------------------------------------------===// 498 // BlockInfo Block Emission 499 //===--------------------------------------------------------------------===// 500 501 /// EnterBlockInfoBlock - Start emitting the BLOCKINFO_BLOCK. 502 void EnterBlockInfoBlock(unsigned CodeWidth) { 503 EnterSubblock(bitc::BLOCKINFO_BLOCK_ID, CodeWidth); 504 BlockInfoCurBID = ~0U; 505 } 506 private: 507 /// SwitchToBlockID - If we aren't already talking about the specified block 508 /// ID, emit a BLOCKINFO_CODE_SETBID record. 509 void SwitchToBlockID(unsigned BlockID) { 510 if (BlockInfoCurBID == BlockID) return; 511 SmallVector<unsigned, 2> V; 512 V.push_back(BlockID); 513 EmitRecord(bitc::BLOCKINFO_CODE_SETBID, V); 514 BlockInfoCurBID = BlockID; 515 } 516 517 BlockInfo &getOrCreateBlockInfo(unsigned BlockID) { 518 if (BlockInfo *BI = getBlockInfo(BlockID)) 519 return *BI; 520 521 // Otherwise, add a new record. 522 BlockInfoRecords.push_back(BlockInfo()); 523 BlockInfoRecords.back().BlockID = BlockID; 524 return BlockInfoRecords.back(); 525 } 526 527 public: 528 529 /// EmitBlockInfoAbbrev - Emit a DEFINE_ABBREV record for the specified 530 /// BlockID. 531 unsigned EmitBlockInfoAbbrev(unsigned BlockID, BitCodeAbbrev *Abbv) { 532 SwitchToBlockID(BlockID); 533 EncodeAbbrev(Abbv); 534 535 // Add the abbrev to the specified block record. 536 BlockInfo &Info = getOrCreateBlockInfo(BlockID); 537 Info.Abbrevs.push_back(Abbv); 538 539 return Info.Abbrevs.size()-1+bitc::FIRST_APPLICATION_ABBREV; 540 } 541 }; 542 543 544 } // End llvm namespace 545 546 #endif 547